THE MADDEN-JULIAN OSCILLATION (MJO) GENERALLY FOLLOWS A PHASE CYCLE (SUPPRESSED DEVELOPING MATURE) EACH CHARACTERIZED BY UNIQUE CLOUD POPULATION DISTRIBUTIONS WIND PATTERNS AND WATER VAPOR DISTRIBUTIONS. SHALLOW CONVECTION DOMINATES THE SUPPRESSED PHASE GRADUALLY DEEPENING CONVECTION AND WATER VAPOR BUILDUP DEFINE THE DEVELOPING PHASE DEEP CONVECTIVE SYSTEMS AND HEAVY RAINFALL PREVAIL DURING THE MATURE PHASE. NEAR SURFACE WINDS AND ATMOSPHERIC CONVERGENCE ALSO VARY AMONGST MJO PHASES AND FEEDBACK TO THE EVOLUTION OF CLOUD POPULATIONS. HOWEVER STORM-SCALE SURFACE WIND VARIATIONS DURING THE MATURE PHASE OF THE MJO ARE POORLY UNDERSTOOD DUE TO OBSERVATIONAL LIMITATIONS ESPECIALLY OVER COMPLICATED TOPOGRAPHIES SUCH AS THE MARITIME CONTINENT. THIS PROPOSED STUDY WILL USE THE SOON-TO-BE-LAUNCHED CYCLONE GLOBAL NAVIGATION SATELLITE SYSTEM (CYGNSS) DATA THE GLOBAL PRECIPITATION MEASUREMENT (GPM) RAINFALL RETRIEVAL AND PRECIPITATION RADAR DATA AND A COUPLED ATMOSPHERE-OCEAN-WAVE REGIONAL MODEL TO INVESTIGATE FEEDBACKS BETWEEN SURFACE WINDS AND CLOUD POPULATION EVOLUTION OVER TWO FOCUS REGIONS: THE INDIAN OCEAN AND THE MARITIME CONTINENT. CYGNSS UNIQUE HIGH RESOLUTION ALL-WEATHER DETECTION CAPABILITY ALLOW US TO ADDRESS THREE PRIMARY RESEARCH QUESTIONS: 1) HOW MUCH DOES THE WIND-DRIVEN SURFACE FLUXES VARY AMONGST THE MJO PHASES AND IN BOTH FOCUS REGIONS? 2) HOW DO CLOUD-SYSTEM SCALE WIND VARIATIONS (E.G. THE CLOUD OUTFLOW GUST FRONT AND COLD POOL) MODIFY SURFACE FLUXES AND MEAN WIND? 3) HOW DO SURFACE FLUX AND ITS DIURNAL CYCLE AFFECT MJO VARIABILITY OVER THE TWO FOCUS REGIONS DIFFERENTLY? TO ADDRESS THESE QUESTIONS BOTH THE MEAN AND DIURNAL VARIATION STATISTICS FROM CYGNSS L2 SURFACE WIND AND MEAN SQUARE SLOPE (MSS) DATA WILL BE COMPILED FOR DIFFERENT MJO PHASES. SURFACE FLUXES WILL BE DERIVED BY COMBINING CYGNSS DATA WITH SEA SURFACE TEMPERATURES AND ATMOSPHERE TEMPERATURE AND WATER VAPOR DATA. CLOUD POPULATION DISTRIBUTIONS AND THEIR CHANGES THROUGHOUT THE MJO PHASES WILL BE EXTRACTED FROM GPM L2 RADAR OBSERVED ECHO TOP HEIGHTS. THE COUPLED OCEAN ATMOSPHERE WAVE SEDIMENT TRANSPORT MODELING SYSTEM [COAWST] WHICH HAS BEEN SUCCESSFULLY USED IN SIMULATING THE DYNAMO (DYNAMICS OF THE MADDEN- JULIAN OSCILLATION) FIELD CAMPAIGN MJO EVENTS IN OUR PREVIOUS STUDY WILL ENABLE US TO IDENTIFY PHYSICAL MECHANISMS AND CORROBORATE HYPOTHESES DERIVED FROM SATELLITE DATA ANALYSES. THIS PROPOSAL ADDRESSES NASA ROSES 2016 PROPOSAL CALL A.23 ITEM 2.2: COMBINE CYGNSS WITH OTHER TROPICAL OCEAN AND ATMOSPHERE OBSERVATIONS AND MODEL OUTPUTS TO CHARACTERIZE AND EXPLAIN THE RELATIONSHIP(S) BETWEEN THE PHASE OF THE MJO AND DIURNAL VARIATIONS IN OCEAN SURFACE WINDS AND FLUXES.